In the field of orthopedics, prosthetic devices, such as artificial joints, are often implanted or seated in a patient's bone cavity. The cavity is typically formed during surgery before a prosthesis is seated or implanted, for example, a physician may remove and or compact existing bone to form the cavity. The prosthesis usually includes a stem or other protrusion that is inserted into the cavity.
To create the cavity, a physician may use a broach conforming to the shape of the stem of the prosthesis. Solutions known in the art include providing a handle with the broach for manual hammering by the physician during surgery to impel the broach into the implant area. Unfortunately, this approach is crude and notoriously imprecise, leading to unnecessary mechanical stress on the bone and highly unpredictable depending upon the skill of a particular physician. Historically, this brute force approach will in many cases result in inaccuracies in the location and configuration of the cavity. Additionally, the surgeon is required to expend an unusual amount of physical force and energy to hammer the broach and to manipulate the bones and prosthesis. Most importantly, this approach carries with it the risk that the physician will cause unnecessary further trauma to the surgical area and damage otherwise healthy tissue, bone structure and the like.
Another technique for creating the prosthetic cavity is to drive the broach pneumatically, that is, by compressed air. This approach is disadvantageous in that it prevents portability of an impacting tool, for instance, because of the presence of a tethering air-line, air being exhausted from a tool into the sterile operating field and fatigue of the physician operating the tool. This approach, as exemplified in U.S. Pat. No. 5,057,112 does not allow for precise control of the impact force or frequency and instead functions very much like a jackhammer when actuated. Again, this lack of any measure of precise control makes accurate broaching of the cavity more difficult, and leads to unnecessary patient complications and trauma.
A third technique relies on computer-controlled robotic arms for creating the cavity. While this approach overcomes the fatiguing and accuracy issues, it suffers from having a very high capital cost and additionally removes the tactile feedback that a surgeon can get from a manual approach.
A fourth technique relies on the inventor's own, previous work which uses a linear compressor to compress air on a single stroke basis and then, after a sufficient pressure is created, to release the air through a valve and onto a striker. This then forces the striker to travel down a guide tube and impact an anvil, which holds the broach and or other surgical tool. However, this arrangement, due to the pressure of the air, results in the generation of large forces on the gear train and linear motion converter components, which large forces lead to premature wear on components.
Consequently, there exists a need for an impacting tool having an improved drive assembly that overcomes the various disadvantages of existing systems and previous solutions of the inventor.